Electronic-trip circuit breakers are used to control the flow of electricity through an electrical distribution system and to protect equipment and personnel from damage or harm in the event of an overcurrent or short-circuit event. Coordination of circuit breaker protection for overload current conditions can be consistently applied as the current constituting an overload condition is relatively low and can be defined according to the known physical and operational parameters of the electrical distribution system. However, coordination of circuit breaker protection for short-circuit conditions can be more difficult as the short circuit current can be inaccurate or difficult to estimate. Inaccuracies in estimation of the available short circuit current can be caused by a number of factors including: inaccurate estimation of short circuit current provided by the utility; transformer, cable, and connection impedances; stray line inductance and capacitance; other rotating machines present on the local electrical grid that can feed the fault; and lighting or other loads that effect system operation.
The advent of electronic-trip circuit breakers, such as the POWERPACT® circuit breakers available from Schneider Electric, brought about the ability to communicate with other control components in the electrical distribution system and to be adjusted through communication systems. Electronic circuit breakers allow for dynamic adjustment of their trip settings for optimized performance, thereby increasing system reliability, reducing potential damage from a short circuit, and preventing improper coordination of overcurrent protective devices in the presence of changes in the electrical distribution system.
U.S. patent application Ser. No. 12/903,540, filed on Oct. 13, 2010, entitled “Method of Estimating Short Circuit Current Available By Analysis of DC Charging Circuit,” describes a method of accurate, real-time estimation of short circuit current available (SCCA) by examining the harmonic content of a non-linear load and correlating the harmonic response to a reference to determine SCCA at the point of monitoring.
What is needed is a way to use accurate SCCA estimation and reporting systems to optimally and automatically coordinate trip settings among circuit breakers in an electrical distribution system using the SCCA estimates.